Sprockets for engaging modular belts are usually made from stainless steel or plastic that is machined or molded. In food processing applications, sprockets are a particularly critical area for cleaning. It is important to be able to periodically remove the residual matters totally from the sprockets and on the rear side of the belt, in order to avoid bacteria growth and spoilage of the food processed on the belt. For this purpose sprockets have been designed with large openings to allow cleaning fluid to pass from the side and reach the critical areas to be cleaned. Such sprockets are disclosed in U.S. Pat. No. Re. 38,607. Typically, the sprocket rim and teeth are covering the hinges and hinder the fluid from reaching the hinge area for proper cleaning. Therefore the sprocket disclosed in the patent further provides pairs of teeth in a double row such that the teeth of a pair are offset. This arrangement allows better cleaning access to the rear belt side and easier release of residual matters collected on the rear belt side. But this design only partially solves the problem since the critical hinge areas are still covered by the sprocket rim to a certain extent, when engaged on the sprocket. Therefore good access to these hinges is of primary importance.
U.S. Patent Publication No. 2004/0222072 proposes to solve this problem by using a sprocket with an oblique shape as illustrated in FIGS. 3A, 3B of the publication. With this design, the teeth will laterally change their position on the rear side of the belt and regularly expose another place on the belt for better cleaning access. Although this is improving cleanability, the proposed solution is still having the shortcoming of periodically covering the hinge completely in a certain position. Another typical feature of the disclosed sprocket is the tracking on the belt by additional teeth engaging in the hinge gaps (FIG. 3B, reference no. 74). During sprocket engagement these teeth enter into the hinge gap between two links and thus push residual matter into this gap, making it again difficult to clean. Also, the drive pockets (reference 72 as shown in FIG. 3A of the publication) of the sprocket are engaging closely over the drive faces which are identical with the center cross bar on the rear side of the belt. The drive surfaces totally covered by the enclosing drive pocket are another place where residuals are physically squeezed in between thus making cleaning more difficult.
Another patent proposing a similar solution is U.S. Pat. No. 6,740,172. The patent does not disclose the drive engagement but discloses sectional sprockets used to laterally shift the engagement area periodically. Accordingly, there is a need for an improved sprocket for easy cleaning that avoids the above described shortcomings.